The present invention relates to a magnetic tape cartridge having a lid that can open and closes an opening portion for drawing out a magnetic tape.
The present application is based on Japanese Patent Applications Nos. Hei. 10-36170, 10-79455 and 10-350136, the contents of which are incorporated herein by reference.
A magnetic tape cartridge has been used as recording medium for computers etc. As an example of such the magnetic tape cartridge, there has been known a magnetic tape cartridge which comprises: a reel; a magnetic tape wound around the reel; and a cartridge case including an upper cartridge and a lower cartridge, wherein the reel is accommodated in the cartridge case so as to be able to rotate. A lid is pivotably attached to the cartridge case so as to be able to open and close an opening portion formed in the cartridge case. When the magnetic tape cartridge is used, the opening portion is opened by the lid so that the magnetic tape may be drawn out of an opening portion.
When the magnetic tape cartridge is not used, the opening portion is closed by the lid. At this stage, a leader tape attached to a tape end is locked at an end surface of the cartridge case in such a state that the magnetic tape is fully wound up onto the reel while the reel is locked by such a lock component as a reel lock so as to prevent unexpected rotations of the reel. Incidentally, the leader tape is an engagement mechanism for such an apparatus as a computer to introduce the magnetic tape into a tape path.
The lid and the locking structure thereof will be described. In the cartridge case described above, the magnetic tape is wound around the reel rotatably mounted, and the leader tape is positioned at the opening portion when the lid closes the opening portion. The reel is comprised of a set of upper and lower reels, in which a gear portion is formed on the outer circumferential portion of the upper reel.
FIG. 1 shows a basic attachment structure of a lid 60. As shown in FIG. 1, the lid 60 is mounted on an upper cartridge 2a through a supporting shaft 14. The lid 60 is urged by a lid spring 65 in a closing direction as indicated by an arrow A. The lid spring 65 is attached to the supporting shaft 14 through a coil portion 65c thereof, and one leg portion 65b is supported by the frame 2d of the upper cartridge 2a while the other leg portion 65a is supported by a recessed portion 67 formed in the lid 60.
The lid 60 has a hole 61 into which a lid lock member 70 for locking the opening or closing actions of the lid 60 is inserted. The lid lock member 70 can vertically slide in the hole 61 in a cartridge thickness direction. The lid lock member 70 is located adjacent to the supporting shaft 14 when the lid 60 is mounted on the upper cartridge 2a. As shown in FIG. 1, the lid lock member 70 is urged by an upward force of a lid lock spring 16 in a direction indicated by an arrow U, to lock the lid 60 so as not to open by the upper end thereof being engaged with a recessed portion formed in the lower cartridge (not shown) when the magnetic tape cartridge is not used.
To ensure high accuracy and flame resistance, the lid 60 and the cartridge case are respectively made of a composite material of polycarbonate and glass fiber. The lid lock member 70 is made of a material excellent in sliding effect, such as POM, in order to reduce friction. The supporting shaft 14 is molded as a part of the upper cartridge 2a for the reasons of accuracy and costs. A shaft hole 63 through which the supporting shaft 14 is passed is molded as a part of the lid 60 for the reasons of accuracy and costs.
FIG. 2 shows positional and kinetic relationship between the lid 60 and the lid spring 65 in a static state where the lid is opened while a certain torque is being loaded on the lid spring 65. As for the kinetic relationship while the lid 60 is opened, a torque Ts1 of the lid spring 65 is applied to the spring bearing portion 68 of the lid 60 to generate a spring force F6. An opening force F5 is applied to the lid 60 through a release lever (not shown) for opening the lid 60. A load F7 is applied on the supporting shaft 14. The load F7 is a difference between the forces F6 and F5. In this magnetic tape cartridge, the Ts1 is set as 140 gfcm in view of parameters of a lid spring which is generally utilized in this magnetic tape cartridge. A radius r of the supporting shaft 14 is 0.2 cm. A distance d1 from the center of the supporting shaft 14 to a point of action of the force F6 is 0.3 cm. A distance d2 from the center of the supporting shaft 14 to a point of action of the force F5 is 1.1 cm.
A relationship among T (torque), F (force), and d (distance) is defined as follows:
T (torque)=F (force)xc3x97d (distance) 
In view of the above, the specific values of F6 and F5 are defined as follows:
F6=Ts1/d1=467 gf 
F5=Ts1/d2=127 gf 
Further, the specific value of F7 is defined based on balance of the forces as follows:
F7=F6xe2x88x92F5=340 gf 
Accordingly, if a static friction coefficient xcexc of the resin is set as 0.52, a friction torque Tf1 of the supporting shaft 14 is defined as follows:
Tf1=F7xc3x97xcexcxc3x97r=35 gfcm 
FIG. 3 shows positional and kinetic relationship between the lid 60 and the lid spring 65 in a static state where the lid 60 is closed. As for the kinetic relationship while the lid 60 is closed, a torque Ts2 of the lid spring 65 is applied to the spring bearing portion 68 of the lid 60 to generate a spring force F2. A counter force Fe is applied from the leader tape 21 to the lid 60. A load F3 applied to the supporting shaft 14 is a sum of F2 and Fl. Incidentally, in this magnetic tape cartridge, the Ts2 is 60 gfcm and the force Fl is 8 gf while the distance d3 from the center of the supporting shaft 14 to a point of action of the force Fl is 4.5 cm.
In view of the above, the specific value of F2 is defined as follows:
F2=Ts2/d1=200 gf 
Therefore, the specific value of F3 is defined based on balance of the forces as follows:
F3=F2+Fl=208 gf 
Accordingly, a friction torque Tf2 of the supporting shaft 14 is defined as follows:
Tf2=F3xc3x97xcexcxc3x97r=22 gfcm 
As a result, a spare torque Tt of the lid spring 65 in the close state of the lid 60 is defined as follows:
Tt=Ts2xe2x88x92(Tf2+T1)=2 gfcm 
(wherein T1=8xc3x974.5=36 gfcm)
That is, the closing action of the lid 60 is maintained by the above torque Tt.
As described above, the material, represented by such as polycarbonate which can ensure the high accuracy and the flame resistance, has a large friction coefficient as a synthetic resin (friction coefficient xcexc=0.4 to 0.6). Therefore, the lid 60 may be stopped in the middle of the pivotal action due to the rotational resistance between the supporting shaft 14 and the shaft hole 63. Further, there is a possibility in that the load is increased on the drive of an apparatus, such as a computer, when the lid 60 is pivoted.
Additionally, when the lid 60 is opened, since the lid lock member 70 moves while the lid lock member 70 is being pushed toward the upper cartridge 2a by the door releasing lever of the drive, thrust friction between the lid 60 and the upper cartridge 2a increases, and therefore the opening operation may require more force and friction powder may be generated. On the other hand, when the lid 60 is closed, since the lid lock member 70 pushes the lower cartridge, the friction occurs between the lid lock member 70 and the lower cartridge, and further, the thrust friction is caused between the lid 60 and the upper cartridge 2a by a counter force applied to the lid 60 by the lid lock member 70. Since the lid 60 and the cartridge case are made of polycarbonate etc. having a large friction coefficient, an imperfect closure of the lid 60 may be caused due to the friction forces as described above, and further, such a serious trouble as a drop out may be caused by the generated friction powder etc.
As described above, such the small spare torque Tt of the lid spring 65 as 2 gfcm is considered to be the reason for the imperfect closure of the lid 60. However, if the spring force of the lid spring 65 itself is increased as a countermeasure against the imperfect closure, the load on the supporting shaft 14 may be increased and the friction may be also increased.
When the force applied to the lid by the lid spring itself is merely increased, the force required for release of the lid is increased, and further, the friction is increased. In addition, the increase in the size of the lid spring itself also increases the storage space for the lid spring. Moreover, after the lid is opened and closed for a large number of times, the friction powder may be generated. The friction powder may result with such a serious trouble as a drop out.
It is possible to eliminate such possibilities as described above by utilization of a material with a better sliding effect, such as polyacetal, in the supporting shaft 14 and also in the shaft hole 63. However, to prevent degradation in the flame resistance and accuracy of the cartridge and the lid, it is necessary to mold the upper cartridge 2a and the supporting shaft 14, as well as the lid 60 and the shaft hole 63, into separate structures or into two colors. In this case, however, there are disadvantages in the accuracy and the costs.
The present invention has been made in view of the background as described above, and an object of the invention is to provide a magnetic tape cartridge realizing smooth pivot of the lid at low cost.
To achieve the above object, according to the first aspect of the present invention, there is provided a magnetic tape cartridge which comprises: a cartridge case including an opening portion, an upper cartridge and a lower cartridge, the upper cartridge having a supporting shaft, and the lower cartridge having a recessed portion; a reel, around which a magnetic tape can be wound, accommodated in the cartridge case, wherein the magnetic tape can be drawn out from the opening portion of the cartridge case; a lid pivotably attached to the supporting shaft in order to open and close the opening portion; a lid spring being a torsion coil spring having a coil portion which is a compressive spring, the lid spring being attached to the supporting shaft through the coil portion so as to urge the lid to close the opening portion; and a lid lock member urged toward the lower cartridge by a lid lock spring so as to be engaged with the recessed portion of the lower cartridge, wherein, when the lid lock member engages with the recessed portion, the lid lock member locks the lid to close the opening portion, and, when the lid lock member is disengaged from the recessed portion, the lid can pivot.
According to the first aspect of the present invention, when the lid is opened, compression of the coil portion results with the counter force working to counter the thrusting force of the release lever and therefore the friction loss between the lid and the upper cartridge is reduced. On the contrary, when the lid is closed, since the lid lock member pushes the lower cartridge, although there is a slight friction between the lower cartridge and the lid lock member made of a low friction coefficient material excellent in sliding effect, a force is generated due to compression of the coil portion and counters the counter force in which the lid lock member pushes the lower cartridge, and therefore the friction loss between the lid and the upper cartridge is reduced. Therefore, the lid can pivot smoothly without being stopped halfway in the course of pivotal movement by the rotational resistance. Additionally, this is realized only by adoption of the compressive spring for the coil portion of the lid spring, and therefore no substantial increase in the cost will result.
The compressive spring herein is a spring which is compressible at the coil portion thereof even if it may resemble ordinary torsion coil springs in the appearance thereof.
Further, according to the second aspect of the present invention, it is preferable that a compressive force of the coil portion of the lid spring is set to be equal to or higher than an urging force in which the lid lock spring urges the lid lock member when the lid closes the opening portion of the cartridge case.
Further, according to the third aspect of the present invention, it is preferable that a compressive force of the coil portion of the lid spring is set to be 1.2 times to 1.5 times higher than an urging force in which the lid lock spring urges the lid lock member when the lid closes the opening portion of the cartridge case.
Still further, to achieve the above object, according to the fourth aspect of the present invention, there is provided a magnetic tape cartridge which comprises: a cartridge case including an opening portion, an upper cartridge and a lower cartridge, the upper cartridge having a supporting shaft; a frame formed on at least one of the upper cartridge and the lower cartridge; a reel, around which a magnetic tape can be wound, accommodated in the cartridge case, wherein the magnetic tape can be drawn out from the opening portion of the cartridge case; a lid pivotably attached to the supporting shaft in order to open and close the opening portion, the lid including a protruding portion; and a lid spring being a torsion coil spring having a coil portion through which the lid spring is attached to the supporting shaft so as to urge the lid to close the opening portion, one leg portion supported by the frame, and the other leg portion supported by the protruding portion of the lid so that a portion of the other leg portion adjacent to an end portion thereof is brought into contact with the protruding portion.
Accordingly, the load on the supporting shaft can be reduced. Consequently, the friction torque of the supporting shaft can be reduced to result with the reduction in the generation of friction powder and with the smooth pivot of the lid. Additionally, this is realized only by provision of the protruding portion on the lid alone and thus no substantial increase in the cost will result. Moreover, since the lid spring is supported at the portion adjacent to the leg end, the torque which applies a force in the direction to close the lid is increased, and therefore, the above-described imperfect closure of the lid can be eliminated.